The Founders did not imagine an electorate as profoundly ignorant as the one we now have.
It’s not so much that the electorate has become so much more ignorant but that who is allowed to vote (who is included in the electorate) has changed so drastically from the time of the founding.
From Wikipedia...
“The United States Constitution did not originally define who was eligible to vote, allowing each state to determine who was eligible. In the early history of the U.S., most states allowed only white male adult property owners to vote.[1][2][3] Women could vote in New Jersey (provided they could meet the property requirement) and in some local jurisdictions in other northern states. Non-white Americans could also vote in these jurisdictions, provided they could meet the property requirement. Freed slaves could vote in four states. Initially, men without property and women were largely prohibited from voting.”
Think what a different country we would have today if those rules still applied, i.e. if the “system” hadn’t been changed.
Because they didn’t see America as a democracy, but as a republic and limited the vote. Those ‘elevator brakes’ have been removed and we’re plunging.